Disposable absorbent products have been known for some time, including such products as disposable diapers, sanitary wound dressings, bandages, incontinent pads, and the like. These products incorporate an absorbent batt or panel that is used to absorb and hold or contain body fluids. In years past, in many of these products, especially diapers and sanitary napkins, the absorbent batt comprised what is termed "wadding" or plies of tissue. The wadding was disposed between an impermeable backing sheet and a permeable facing sheet and the plies of tissue were used to absorb and contain the liquid within the product.
The wadding type of batt was replaced, for the most part, by an improved absorbent batt comprised of fluffed wood pulp fibers. This absorbent batt comprises a layer of individualized wood pulp fibers with the layer having substantial thickness. This diaper has improved absorbent capacity and has somewhat better containment than a diaper using a wadding layer. Also the fluffed wood pulp layer is quite soft, flexible and conformable and hence, produces an improved diaper over diapers using wadding as the absorbent layer.
Though the fluffed wood pulp absorbent batts have improved capacity, the efficiency with which the capacity is used in a diaper is poor. The reason for this, is that the fluid to be absorbed is generally deposited in a localized or a target area within the absorbent batt and the ability for the fluid to wick along the plane of the batt is poor. The fluid follows the path of least resistance and consequently moves to the closest edge of the batt where it generally is no 10 longer contained and the product leaks. Furthermore, the wood pulp batts lack stability, e.g., when a diaper is being worn, the batt tends to sag and/or break up thereby creating bunching.
U.S. Pat. No. 3,017,304 discloses an absorbent product which incorporates in the batt a densified, paper-like layer. This paper-like layer acts as a wick, i.e., liquid which contacts the layer tends to move rapidly along the plane of the layer. When incorporated in combination with fluffed wood pulp fiber, the resultant product uses the absorbent capacity of the fluffed wood pulp much more efficiently. Diapers which incorporate this paper-like layer combined with fluffed wood pulp are disclosed and described in U.S. Pat. Nos. 3,612,055 and 3,938,522. Even though these products make much greater use of the capacity of the absorbent batt, they still do not totally contain the absorbed liquid.
A number of years ago "superabsorbent materials", i.e., materials which will absorb many times their weight of liquid, were developed. Since the development of such materials, various different approaches have been suggested to incorporate them in absorbent products such as diapers to enhance the absorptive performance of these products. Perhaps one of the first proposals to incorporate such a superabsorbent material in a disposable diaper is disclosed in U.S. Pat. No. 3,670,731. This patent discloses an absorbent dressing comprising an absorbent layer sandwiched between a permeable facing sheet and an impermeable backing sheet. The absorbent layer contains water insoluble cross-linked hydrocolloid polymer as the superabsorbent material.
In order for a superabsorbent material to function, the liquid being absorbed must be transported 10 to the superabsorbent material. In other words, the superabsorbent material must be placed in a position to be contacted by the liquid discharged onto the absorbent body. Furthermore, as the superabsorbent material absorbs the liquid, it must be allowed to swell. If the superabsorbent is prevented from swelling, it will cease absorbing liquid. Hence, if the superabsorbent material is to function in diapers wherein the liquid to be absorbed is discharged in a small void area, the structure of the absorbent layer containing superabsorbent materials appears to be critical. Over the years a number of techniques have been disclosed in an attempt to provide structures which make efficient use of the superabsorbent material. Such products are typified by those disclosed in U.S. Pat. Nos. 4,103,062, 4,102,340 and 4,235,237. In addition, methods for incorporating superabsorbents into suitable layers or suitable configurations which can be placed in an absorbent product have been proposed, and examples of such proposals are disclosed in U.S. Pat. Nos. 4,186,165, 4,340,057 and 4,364,992.
In United Kingdom Patent Specification No. 1,406,615, published on Sep. 17, 1975, an absorbent pad for use in a disposable diaper is disclosed that includes a wood pulp batt of substantially uniform thickness having a gelling agent or superabsorbent material impregnated in one part (target area) of the batt to the exclusion of, or to a greater extent than in, another part of the batt. In accordance with a preferred embodiment, the superabsorbent material is impregnated in a central area of the pad where it is most effective rather than spreading the material evenly throughout the pad area which is deemed to be uneconomical. The weight of the superabsorbent material in the central area is disclosed as being between 20 percent and 100 percent of the weight of the pad in the central area before impregnation.
In U.S. Pat. No. 3,661,154, an absorbent structure for use in a disposable diaper is disclosed that includes a layer of a blend of cellulose fibers and superabsorbent material. The superabsorbent material concentration is disclosed as being about 1 to 50 parts per 100 parts of cellulose fibers. In accordance with a disclosed embodiment, an additional layer of the cellulose fibers or a layer of a blend of cellulose fibers and superabsorbent material is superimposed on the base layer. This additional layer may be narrower than the base layer and it may be disposed along the central portion of the diaper at the area most likely to be wetted (target area). The additional layer may be the same thickness as, or thicker or thinner than, the base layer.
In U.S. Pat. No. 4,381,782, an absorbent panel is disclosed that includes a web or batt of a low-density, highly absorbent filler material, such as fluff, to which superabsorbent material is incorporated thereinto in a central area near the front edge of the panel. The side portions of the panel are cut and folded over the central area of the panel.
More recently, other very similar absorbent structures that are directed to making efficient use of the superabsorbent material are disclosed in U.S. Pat. Nos. 4,699,619, 4,673,402 and 4,685,915. In U.S. Pat. No. 4,699,619 various absorbent structure embodiments are disclosed which comprise at least two layers of cellulosic fibers of different densities, with the higher density layer lying beneath a back portion of the lower density layer. In certain embodiments a layer of superabsorbent material is located beneath the higher density layer. In U.S. Pat. No. 4,673,402 an absorbent structure is disclosed that includes an upper layer of essentially hydrophilic fiber material and a lower layer of a substantially uniform combination of hydrophilic fiber material and discrete particles of substantially water-insoluble hydrogel material. The lower layer is positioned such that at least about 75% of the hydrogel material in the lower layer is found within the front two-thirds section of the absorbent structure and such that at least about 55% of the total hydrogel material in the lower layer is found within the front half section of the absorbent structure. In U.S. Pat. No. 4,685,915 an absorbent structure is disclosed that includes a layer of cellulosic fibers which is so disposed that the central portion has a greater average density per unit area and a greater average basis weight per unit area than each of the end portions. Hydrogel particles may be either uniformly dispersed or may be dispersed primarily or only in the central portion of the absorbent structure.
It has heretofore been proposed to provide absorbent panels for disposable diapers that have predetermined regions of increased fiber basis weight. In U.S. Pat. No. 3,848,598 an absorbent batt is disclosed that is made of cellulosic fibers and formed convexly about the transverse and longitudinal medians thereof. In U.S. Pat. No. 3,766,922 gender specific absorbent structures are disclosed that are made of cellulosic fibers and have predetermined regions of differing fiber basis weight. Valleys and/or ridges are embossed in certain of the regions. In U.S. Re. No. 29,789 an absorbent structure is disclosed having a medial portion of greater basis weight than flanking end and side portions. In U.S. Pat. No. 4,971,852 a cellulosic fiber-containing absorbent batt is disclosed that is longitudinally and transversely contoured by the use of a scarfing roll. There is no disclosure or teaching of forming longitudinally elongated grooves in the batt.
In U.S. Pat. No. 4,670,011 an absorbent batt is disclosed that includes upper and lower fibrous webs superposed to define a web interface therebetween. Superabsorbent particles are disposed in discrete longitudinally spaced apart regions at the interface.
In published PCT Application PCT/DK85/00081 (WO86/01378) a fibrous absorbent pad is disclosed that has a plurality of rectilinear and parallel channels that extend over the entire length of the structure. The channels are disclosed as being formed by cutting or milling and having a depth of 65-95% of the thickness of the pad.